Hardening of metal surfaces



Patented Apr. 18, 1939 UNITED STATES.

PATENT OFFICE HARDENING F METAL SURFACES No Drawing. Application June 17, 1937, Serial No. 148,753. In Great Britain June 20, 1936 1 Claim.

This invention relates to the production of cast-iron articles (and particularly rails for supporting machine-tool or other slides) having a hardened surface, the hardening being effected 5 by local heating of the surface, by means of a burner, to a high temperature whereafter the heated part of the surface is immediately cooled.

The flame from the burner is progressively applied to the surface at a predetermined rate, the 0 arrangement being such that there is not sumcient time for the heat to be conducted away to the interior of the article before the surface of the latter is quenched.

The present invention broadly involves using a grey cast iron and casting in such a way that the surface to be hardened is rendered dense; whereafter the surface of the cast metal is treated, in a known manner, by being locally heated, by means of a burner, to a, high temperature and then immediately cooled.

In the case of a cast-iron article formed by a centrifugal casting operation the outer surface is normally rendered dense during the casting operation.

In the case of a die casting operation, the die can be arranged to provide a local chilling or densening effect at the surface of the article which is subsequently to be hardened.

In the case of a sand casting operation, however--for example, in the production of castiron rails for lathe bedschills or denseners are arranged in a manner known per se adjacent the surface of the article which is subsequently to be hardened.

In a preferred method of forming cast-iron rails for lathe beds, according to the invention, the iron used, which is to be cast in a sand mould, is one having the following analysis:

Per cent Total carbon 2.5 to 3.5 Combined carbon 0.4 to 1 Silicon 0.9 to 2.5 Manganese 0.3 to 1.3

Sulphur 0.06 to 0.15

Phosphorus 0.2 to 1.2

Nickel may with advantage be added up to, say,

5%, the percentage preferably not being less than 1.25%.

When the sand mould is set up the necessary chills or denseners are disposed at the bottom, these consisting of metal bars of, say, 32 mm. depth and of a width substantially equal to that of the rails to be cast. The depth of the bars would be between 13 mm. and 39 mm. dependent upon the composition of the metal and the type of casting. Use is preferably made for each rail of a number of denseners arranged in line but spaced slightly from one another. The upper surfaces thereof are arranged to conform to that of the rail to be cast. As will be well understood, when the cast metal is poured into the mould an operative surface of the rail (that is, the lower surface in the mould) contacting with the denseners cools more rapidly than the remainder of the rail and thus produces a dense operative surface.

Thereafter when the cast rails have been formed their operative surfaces are hardened by local heating and quenching in a known manner.

-For this purpose use is preferably made of a combined burner and cooler of the kind de- 25 scribed in our co-pending application No. 148,752, the rail being mounted horizontally and the combined burner and cooler being progressively traversed along it.

By means of the invention very satisfactory 30 hardened surfaces can be produced on cast-iron articles. Although the invention has been particularly described in connection with the formation of lathe bed rails it should be understood that it is not restricted in this respect. 35 

